This invention relates to improvement in apparatus used for injecting pile into ground using hydraulic cylinder system in foundation works.
Installation of pile into ground by various methods have been known for a long time. Installing pile by injecting it into ground using a hydraulically operated apparatus has been developed and improved upon.
Previously known apparatus employ single or multiple hydraulic cylinders in various configurations to inject pile into the ground by a direct application of force exerted by an actuating rod attached with a drive head. The barrel of the hydraulic cylinder is generally disposed above a pile to be worked, so that the actuating rod exerts a force to push the pile downward. This configuration requires a vertical support structure that is much taller than the pile, and suffers the disadvantages of headroom limitation and instability in shift
One known apparatus has a single hydraulic cylinder positioned at the back of the pile with the drive head and a thrust plate connected by a thick plate. This, as in any single cylinder configuration, is unable to inject the whole length of pile into the ground without using a dolly. This exercise of using a dolly is time consuming and needs extra labour force. Multiple hydraulic cylinders are then used, as in another previously known apparatus, with a staggered configuration that enables the whole length of the pile to be injected without a dolly. This apparatus requires a tall and sizable vertical support structure to accommodate this complex multiple cylinder configuration.
Previously known apparatus is suitable for piles of shorter lengths i.e. 3 m to 6 m, and small sizes of 150 to 200 mm. Short piles have to be joined, normally by welding, hence are costly and time consuming. Joints in pile are also inherent weak points. Excessive joints are not encouraged especially in foundation of a new structure.
The present invention aims to provide a better alternative to known apparatus for injecting pile or the like by obviating the disadvantages highlighted above.
The invention provides a strong vertical support structure mounted either on to a platform or a movable carriage, with two hydraulic cylinder barrels positioned vertically side by side having a space in between them to accommodate a pile to be worked. The hydraulic cylinder barrels are disposed such that the end of two actuating rods are fixed rigidly to an uppermost horizontal member on top of the vertical support structures.
Previously known apparatus utilises hydraulic cylinder barrels in the conventional manner, such that the cylinder barrel is fixed and the actuating rod is movable with an attachment to exert a pushing or pulling force. The present invention is characterised in which the hydraulic cylinder barrels are disposed in reversed orientation to that of the conventional manner. The rod becomes fixed while the cylinder barrel is allowed to slide along a guide. One drive head adjoins the top ends of the two cylinder barrels. Another drive head adjoins the bottom ends of the two cylinder barrels.
The vertical support structure has to be strong to resist bending or buckling. It is fabricated preferably using two number of heavy steel H columns and joined at regular intervals with horizontal members. An uppermost horizontal member is a strong steel H section welded rigidly to the two larger vertical H columns. A winch and a hook is attached to the upper part of this uppermost horizontal member. The end of the two hydraulic actuating rods are attached to the bottom part of the uppermost horizontal member, preferably by bolts and nuts.
Two drive heads are used in this present invention. An upper drive head adjoins rigidly the two cylinder barrels at their mouths (top). This upper drive head is thick enough to account for the difference in length between the barrel and the rod of the cylinder, enabling a lower drive head to be locked in position during a second stroke. A cap is incorporated under the upper drive head for positioning the pile centrally between the two cylinder barrels during pitching. The lower drive head has an open and lock-in mechanism and is located at the base of the barrels. The two hydraulic cylinder barrels slide along the two vertical H columns with U section welded to the side as guides.
Retracted hydraulic cylinder barrels will have a length longer than half the length of a pile to be injected. Thus, when fully extended, its length will be longer than the pile, so that the whole pile can be injected into the ground. A complete piling operation involves two strokes. A first stroke commences, using the upper drive head to inject the pile. A second stroke then follows, employing the lower drive head. At the commencement of the first stroke, the cylinder barrels are fully retracted and the head of the pile to be worked is disposed directly beneath the upper drive head. The lower drive head is in xe2x80x98openxe2x80x99 position, allowing the pile through to reach the upper drive head.
The pile is centrally positioned and checked for verticality before a clamp at the lower portion of the support structure is locked in position to restrict any lateral movement of the pile. The simultaneous downward movement of the two cylinder barrels is exerting a force on the pile head through the drive head, pushing the pile into the ground. At the end of the first stroke, half the pile will be injected into the ground when the two hydraulic cylinder barrels are fully extended. The second stroke commences after the cylinder barrels are once again fully retracted and the lower drive head is locked in position by a mechanism. The downward movement of the two barrels is then repeated, but this time the force is exerted through the lower drive head. The whole length of the pile will be injected into the ground at the end of second stroke. The whole operation may be repeated when an extension pile is pitched and positioned beneath the upper drive head with the help of winch located at the top. Joining of piles could be carried out by welding or other means depending on the type of pile used.
It is the aim of present invention to drive piles of larger dimension and length. This is achieved by using hydraulic cylinder barrels of larger bore and length, and with the rods in compression, the downward force is enhanced. Larger or longer piles will pose problem during pitching, and greater effort is needed to prevent them from swinging around which may damage the hydraulic cylinders, especially the extended rods. In this present invention, the pile is positioned below the upper drive head and within a chamber formed by the drive head and the two cylinder barrels. The smooth rod surface is protected and does not come in contact with the pile.
The present invention can be further modified to inject pile by gripping it down. In this case, a gripping device is firmly attached to the cylinder barrels, preferably at the top or the base. The two drive heads are removed and replaced by the gripping device; the pile is pitched as before but placed through the gripping device, With the pile tightly gripped, the downward movement of cylinder barrels will cause the pile to inject into the ground. The grip is then loosened and the cylinder barrels retracted to original position, and the whole operation is repeated
The present invention, if mounted on a base frame, will require a reaction load larger than the jacking force. Known reaction loads include concrete blocks or thick steel plates which are placed symmetrically with its centre of gravity in line with the jacking force. The base frame is equipped with at least four number of stabilising jacks for level adjustment, and rollers or steel pipes to allow lateral movement for pile centering. Alternatively, the present invention can be mounted onto a moving carriage like crawler crane or hydraulic excavator. In this arrangement, part of the reaction load is contributed by the machine dead load. It is possible to transfer some of this reaction load to the back of the machine, if a steel cable or chain fixed firmly and parallel to the vertical support structure and passing through a pulley, is pulled by the loading drum of the crane or a hydraulic cylinder barrel fixed onto the main same of an excavator.